8. SYSTEM INTEGRATION OF VARIABLE RENEWABLE ENERGY

Table 8.1 VRE capacity, generation and percentage share, VRE-rich states, 2018

Sources: CEA (2019a), Renewable Energy Generation Report, March 2019, http://cea.nic.in/reports.html (actual VRE electricity generation from April 2018-March 2019); MNRE (2019), Total Installed Capacity, https://mnre.gov.in/physical-progress-achievements (VRE installed capacity as of 31 March 2019).

In Phase 3 states, VRE determines the operation of the system and flexible resources are needed for improved power system flexibility. In this phase, renewables forecasting and scheduling improvements, dispatch-balancing process review and other changes may be required alongside the activation of advanced flexibility resources, such as improved cross-border trade, storage and demand-side flexibility. Moreover, these states will be transitioning to Phase 4 in the coming years. Only a few parts of the world had reached Phase 4 by 2018, including Ireland, Denmark and South Australia. Their experience shows that a variety of sources of flexibility need to act together: ancillary services reform, the advanced activation of storage and demand-side resources, forecasting and scheduling, and flexibility requirements from VRE.

General considerations for system integration

System integration of renewable energy encompasses all the technical, institutional, policy and market design changes that are needed to enable the secure and cost-effective uptake of large amounts of renewable electricity in the system. The necessary adaptations are most significant for the integration of VRE technologies, namely wind and solar power.

The physical nature of electricity requires that generation and consumption are in balance at all times. System planning and operation need to ensure this, respecting the technical limitations of all system equipment under all credible operating conditions, including unexpected events, equipment failure and normal fluctuations in demand and supply.

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8. SYSTEM INTEGRATION OF VARIABLE RENEWABLE ENERGY

The difficulty (or ease) of increasing the share of VRE in a power system depends on the interaction of two main factors: the properties of VRE generators; and the flexibility of the power system into which they are deployed (a more detailed discussion can be found in IEA [2014; 2016]).

Different timescales of system flexibility requirements

Power system flexibility is defined as the ability of a power system to reliably and costeffectively manage the variability and uncertainty of demand and supply across all relevant timescales, from ensuring instantaneous stability of the power system to supporting longterm security of supply (IEA, 2018b; IEA, 2019c). Challenges for system integration and system flexibility can be categorised along different timescales:3

In the medium to long term the key flexibility requirements relate to the availability of sufficient power system resources (generation, demand response, storage and imports from other areas of the grid) to reliably meet demand.

In the short term the power system requires the ability to maintain the balance of supply and demand in the face of variability and uncertainty of both supply and demand. In order to achieve this, the power system needs sufficient flexible resources that can change their output quickly, at short notice and in a wide range from within a few minutes to several hours.

In the very short term the power system needs to withstand disturbances from within the first milliseconds to several seconds following a load or generation change event, also referred to as stability.

Achieving high shares of wind and solar power in a costeffective and reliable way

Given the broad impacts that high VRE shares can have, a comprehensive and systemic approach is the appropriate answer to system integration challenges. As identified by IEA analysis, a co-ordinated approach can significantly reduce integration costs and ensure electricity security (IEA, 2014; IEA, 2016). Achieving such a transformation requires strategic action in three main areas:

System-friendly deployment to maximise the net benefit of wind and solar power to the entire power system. This could, for example, mean prioritising VRE deployment with a greater contribution to peak load periods or locations close to load centres rather than focusing on VRE cost of production alone.

Improved operating strategies as a tool to maximise the contribution of existing assets and ensure security of supply. These include advanced renewable energy forecasting and enhanced scheduling of power plants. Where liberalised wholesale markets are in place, this may require an upgrade of market rules and products. In heavily regulated systems, action will need to target operational protocols and key performance indicators for system and power plant operators.

Investment in additional flexible resources. Even in concert, improved operations and system-friendly VRE deployment practices can be insufficient to manage very high shares of VRE in the long term. The point at which investment in additional flexible resources

3 Based on detailed description in IEA (2018b).

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